Recent housing, of which so-called “smart houses” are representative, is being built with the aim of achieving comfort without carbon dioxide emissions under keywords such as “energy saving,” “energy creation,” and “energy storage.” Meanwhile, the concept of the “passive house” exists. In relation thereto, the building of housing with high heat insulation performance for extensive energy saving and comfort has been gaining attention. In any housing, it is indispensable to improve performance in the areas of heat insulation and thermal environment. Against such background, research and development of building materials that allow heat to be stored via the floors and walls of housing so as to provide a comfortable living space while saving energy have been gaining momentum.
For example, there have been proposals and attempts to store the natural energy of sunlight or the like, thermal energy generated by heating and cooling equipment or the like, heat energy generated in daily living, and the like in latent heat storage material that can realize heat absorption or dissipation depending on changes in exterior air temperature, so as to minimize interior temperature change.
For example, Patent Literature 1 to 6 disclose technology combining building materials with latent heat storage material for imparting heat storage ability to building materials. Patent Literature 1 discloses a technology of dispersing microcapsules encapsulating a latent heat storage material in solid media such as cellulose fibers. Patent Literature 2 discloses a technology of allowing a board comprising a kenaf core to absorb a latent heat storage material. Patent Literature 3 discloses a technology of incorporating a latent heat storage material into a matrix comprising an inorganic cement material. Patent Literature 4 discloses a technology of dispersing pellets containing a latent heat storage material within a substrate such as plaster, concrete, or the like. Patent Literature 5 discloses a technology of laminating a heat storage sheet impregnated or coated with microcapsules encapsulating a latent heat storage material on an interior face or another face of plasterboard. Patent Literature 6 discloses plasterboard made of a porous material or the like that is impregnated with a molten mixture comprising an ethylene-α-olefin copolymer having given densities and a heat storage material.
Using latent heat storage materials means using the latent heat required for phase transition between the solid phase and the liquid phase. When using the materials, liquid efflux can sometimes cause problems. If a porous substrate is impregnated merely with a latent heat storage material, as in the case of Patent Literature 2, it is impossible to avoid the exudation (that is, efflux) of the latent heat storage material from the porous substrate at temperatures equaling or exceeding the melting point of the latent heat storage material. In view of this, Patent Literature 4 discloses that the pellets are formed by dispersing the latent heat storage material within the polyolefin matrix, thereby reducing exudation of the latent heat storage material during melting. Also, Patent Literature 6 discloses that addition of an ethylene-α-olefin copolymer having a given density reduces exudation of the latent heat storage material. However, the conventional technology for preventing exudation of a latent heat storage material from a porous substrate is not sufficient. Accordingly, there is a demand to further improve such technology.
Patent Literatures 7 to 11 disclose the technology of preventing latent heat storage material exudation by combining a latent heat storage material, such as paraffin, with a polymer compound. However, Patent Literature 7 to 11 do not suggest using the latent heat storage material composition to impregnate porous substrates, such as a wooden building material. These literatures only teach using the composition by itself as a heat reservoir. Such heat storage material composition has a high viscosity upon melting, thus not allowing a porous substrate to be impregnated therewith. This has been problematic.